This invention relates to a surgical cutting instrument of the type employing rotary cutters. Instruments of this type are usable for various surgical procedures in various regions of the body, such as in the eye and knee. For example, such surgical cutting instruments may be inserted through a small opening into the knee joint and used for cutting the meniscus or other soft or hard material or tissue.
Generally, a surgical cutting instrument of this type includes an outer tube having a peripheral wall, an end wall, at least one opening in one or both of the peripheral wall and the end wall and a cutting edge defining at least a portion of the periphery of the opening. An inner cutting member, which may also be in the form of a tube, rotates or translates within the outer tube. The inner cutting member has a cutting edge that cooperates with the cutting edge or edges of the outer tube for cutting material with a shearing action as the inner cutting member is moved relative to the outer tube. One surgical cutting instrument of this general type is shown and described in Johnson et al U.S. Pat. No. 4,274,414.
Another cutting instrument of this type is the whisker cutter. In this instrument, the outer tube has a plurality of small circular openings to adapt the instrument for cutting fine hair-like projections, such as synovial tissue, from within the knee. The whisker cutter is also useful in a trimming or finishing step after the bulk of the tissue has been cut by a more aggressive cutter. Thus, for example, the main cutting is done with an aggressive cutting instrument which is then removed from the patient. The whisker cutter is then inserted into the same opening in the patient to perform the trimming or finishing. The use of two or more separate cutters is not only time consuming, but also can cause substantial additional trauma to the patient in general and to the surgical site in particular. While the whisker construction is satisfactory for certain applications, it is not suitable for a broader range of applications. For example, the round edges of the circular small holes of the outer tube do not provide as good a scissors or shearing action as is desirable for some applications.
One type of inner cutter which has been suggested is a helical or auger cutter. For example, Banko U.S. Pat. No. 4,167,944 uses a helical cutter at the distal end of a device having a outer tube with a single circular opening. Staub, et al U.S. Pat. No. 4,014,342 uses an elongated helical cutter in conjunction with an outer tube having a single opening in the distal end thereof. Thimsen, et al U.S. Pat. No. 4,649,919 uses a helical cutter in combination with an outer sheath which is open at its distal end and proximally therefrom to form diametrically opposed tabs with inwardly extending lips. Pippin, U.S. Pat. No. 3, 308,828 and Perrill U.S. Pat. No. 2,532,370 use helical cutters in conjunction with outer protective shields which do not have cutting edges or surfaces. These devices tend to become clogged with material removed from the patient's body and/or, because of the geometry of certain of these devices, are somewhat difficult to insert in the patient's body. Also, many of these devices provide end cutting or side cutting, but not both.
Notwithstanding a proliferation of known configurations for the outer tube and the inner cutting member, there are problems with poor cutting ability and inconsistent quality. In addition, cutting instruments are often classified as either aggressive cutters or non-aggressive cutters, and are not useful for both aggressive cutting and trimming or finishing, both of which may be necessary in a single surgical procedure.